One thing sorely missing in MacOS is a visual indicator for which pane is active (I don't mean textboxes). For example, using Mail.app in column view: if I click on a message in the list, then the contrast makes it obvious that I'm focused on the message, and if I use the arrow keys then I'll move to the previous or next message. But if I press tab, the focus goes into the message contents pane; I know I'm no longer focused on the message list, but I also can't be sure that I'm focused on the contents pane.